How Is Friction Unhelpful?
Friction is a force that opposes motion, so it is unhelpful in all situations where the motion of an object is desired. A by-product of friction is that energy is wasted in the form of heat, which can cause problems in temperature-sensitive environments.
Situations where friction is undesired include the friction in wheels that slows them down, the air resistance against a car that leads to reduced fuel efficiency and friction on bike chains that make them hard to pedal.
Friction is caused by the interaction between two surfaces. The amount of friction generated is dependent upon the hardness of the surfaces that are in contact with each other, the roughness of the surfaces and the size of the contact area.